Appunti di storia dei logaritmi. VI: La svolta euleriana

In this paper, that closes the series of papers devoted to the history of logarithms, I outline the main contributions given by Euler. In particular, I examine his theory of logarithms of negative numbers that brilliantly solved, by the mid 1700s, a controversy, raised some forty years earlier between Leibniz and Johann Bernoulli. In the last section of this paper, a sort of divertissement, I follow the funny history of a result of Mengoli’s that reappeared now and again - although no one aknlowledged its author - and that is related to the Euler-Mascheroni constant.